Benzothiazole sulfenamides

ABSTRACT

COMPOUNDS OF THE FORMULA   ((X-BENZOTHIAZOL-2-YL)2-N-S)N-R   WHEREIN X IS HYDROGEN, ALKYL ALKOXY, NITRO, HALO, OR HYDRXY AND N IS ONE OR TWO; WHEN N IS ONE R IS ALKYL, CYCLOALKYL, ARALKYL OR ARYL; WHEN N IS TWO R IS ALKYLENE WHICH COMPOUNDS ARE DELAYED ACTION CURE ACTIVATORS FOR RUBBER.

United States Patent 01 fice 3,689,467 Patented Sept. 5, 1972 3,689,467 BENZOTHIAZOLE SULFENAMIDES Kamel Boustany and John J. DAmico, Akron, Ohio, assignors to Monsanto Company, St. Louis, M0. N0 Drawing. Filed Jan. 28, 1971, Ser. No. 110,658 5' Int. Cl. C08c 11/62; C08f 27/06 US. Cl. 260--79.5 B 11 Claims ABSTRACT OF THE DISCLOSURE Compounds of the formula alkyl, aralkyl or aryl; when n is two R is alkylene which 20 compounds are delayed action cure activators for rubber.

N--S R BACKGROUND OF THE INVENTION This invention relates to new compounds useful as activators for the vulcanization of rubber.

Activators, sometimes called secondary accelerators, are used by manufacturers of vulcanized products to improve the vulcanization process by reducing the time required to cure a vulcanizable composition. Commonly used activators are diphenylguanidine and thiuram sulfides, however, their use adversely aifects the processing safety of the stocks and as a consequence, prevulcanization inhibitors may have to be used to avoid premature vulcanization of certain stocks. The compounds of this invention possess a valuable combination of properties in that they activate the vulcanization cure rate and also inhibit premature vulcanization. These and other advantages of the invention will become apparent as the description of the 40 invention proceeds.

SUMMARY OF THE INVENTION The compounds of this invention are characterized by the formula wherein X is hydrogen, lower alkyl, lower alkoxy, nitro, chloro, bromo, iodo, or hydroxy and n is one or two; when n is one R is alkyl, cycloalkyl, aralkyl or aryl; when n is two R is alkylene. The alkyl radical may be primary, secondary or tertiary and the alkyl chains thereof may be branched or unbranched. Alkyl radicals of 1-20 carbon atoms are suitable with radicals of 1-10 carbon atoms being preferred. According to this invention lower alkyl means radicals of l-5 carbon atoms. Cycloalkyl radicals of 5-12 carbon atoms are suitable with radicals of 5-8 carbon atoms being preferred. Aralkyl is a monovalent alkyl radical having a phenyl radical attached to a carbon atom of the alkyl chain. Aralkyl radicals of 7-10 carbon atoms are preferred. Aryl is a monovalent radical derived N-S R by removal of one hydrogen atom from an aromatic hydrocarbon. The aryl radical may be substituted in the aromatic nucleus by alkyl groups. Aryl radicals of 6-12 carbon atoms are suitable. Phenyl is the preferred aryl radical but radicals of the naphthalene series are suitable. Alkylene means a divalent alkyl radical wherein each valence is attached to an acyclic or cyclic aliphatic carbon atom. Alkylene radicals of 1-8 carbon atoms are preferred. The alkylene chain may be interrupted by a phenylene radical.

Examples of R are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, cert-butyl, amyl, hexyl, octyl, decyl, dodecyl, cetyl, eicosyl, cyclopentyl, cyclohexyl, cyclooctyl, cyclodecyl, cyclododecyl, benzyl, alpha-methyl benzyl, alpha,alpha-dimethyl benzyl, phenethyl, xylyl, phenyl, naphthyl, tolyl, 4-ethyl phenyl, ethyltolyl, propylphenyl, butylphenyl, hexylphenyl, methylene, dimethylene, trimethylene, l-methyldimethylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, octamethylene, l,4-dimethyltetramethylene, xylylene and cyclohexylene.

Examples of the compounds of the invention are:

N,N-di (4-methylbenzothiazolyl) cyclohexanesulfenamide,

N,N-di S-ethylbenzothiazolyl alpha-toluenesulfenamide,

N,N-di 4-chlorobenzothiazolyl benzenesulfenamide,

N,N-di S-bromobenzothiazolyl isopropanesulfenamide,

N,N-di 6-ethoxybenzothiazolyl )-n-butanesulfenamide,

N,N-di 6-nitrobenzothiazolyl) -2-isobutanesulfenamide,

N,N-di (6-hydroxy benzothiazolyl cyclohexanesulfenamide,

N,N-di (2-benzothiazolyl methanesulfenamide,

N,N-di (Z-benzothiazolyl ethanesulfenamide,

N,N-di 2-benzothiazolyl -n-butanesulfenamide,

N,N-di (Z-benzothiazolyl) octanesulfenamide,

N,N-di Z-benzothiazolyl alpha-toluenesulfenamide,

N,N-di (2-benzothi azolyl )-p-toluenesulfenamide,

N, N-di (Z-benzothiazolyl naphthalenesulfenamide,

N,N-di (2-benzothiazolyl cyclopentanesulfenamide,

N,N-di (2 benzothiazolyl) cyclododecanesulfenamide,

N,N-di (2-benzothiazolyl) -2-isobutanesulfenamide,

N ,N-di (4-methyl-2-benzothiazolyl benzenesulfenamide,

N,N-di 5-chloroZ-benzothiazolyl) propanesulfenamide,

1,2-bis[N,N-di Z-benzothiazolyl aminothio] ethane,

1,4-bis [N ,N-di (2-benzothiazolyl aminothio] butane,

1,6-bis [N,N-di (Z-benzothiazolyl) aminothio] hexane,

1,4-bis[N,N-di(2-benzothiazolyl)aminothio1cyclohexane and bis [N,N-di 2-b enzothiazolyl) aminothio] phenylenedimethylene.

Compounds wherein n is one are prepared by reacting a sulfenyl chloride with a 2,2'-iminobis(benzothiazole); substituting a his sulfenyl chloride in the same reaction gives compounds wherein m is two.

The compounds of this invention are excellent delayed action activators for the vulcanization of rubber. The addition of the new compounds to sulfur-vulcanizable compositions provides stocks which cure faster with greater processing safety. Both properties are advantageous to the rubber manufacturer since faster cure rates decrease the time an article remains in the vulcanization mold, hence increasing productivity; and greater processing safety eliminates discarding of stocks mined by premature vulcanization.

The activators of the invention can be used in natural and synthetic rubbers and mixtures thereof. Any diene rubber having sufiicient unsaturation to be sulfur vulcanizable is suitable. Examples of suitable synthetic rubbers are styrene-butadiene copolymer (SBR), isobutyleneisoprene copolymer (butyl), ethylene-propylene diene terpolymer (EPDM), butadiene-acrylonitrile copolymer (nitrile), polymers of chloroprene (neoprene) and synthetic polybutadiene, particularly cis-polyisoprene and cis-polybutadiene.

The invention is applicable to vulcanizable compositions containing vulcanization accelerators of various classes and accelerator mixtures. For example, rubber mixes containing the aromatic thiazole accelerators which include N-cyclohexyl2benzothiazolesulfenamide, N,N-dialkyl-Z-benzothiazolesulfenamide, Z-mercaptobenzothiazole, N-tert-butyl-2-benzothiazolesulfenamide, 2-benzothiazolyl diethyldithiocarbamate, 2,2-dithiobisbenzothiazole, 2-(morpholinothio)benzothiazole and 2-(morpholinodithio)benzothiazole may be used. Amine salts of mercaptobenzothiazole accelerators, for example, the t-butylamine salt, morpholine salt or 2,6-dimethyl morpholine salt of mercaptobenzothiazole may be used in the invention. Any of the thiazole accelerators may be used. The invention is applicable to stocks containing amine antidegradants. Rubber mixes containing anticleg- :radants, for example, N-l,3-dimethylbutyl-N'-phenyl-pphenylenediamine, N,N bis(l,4 dimethylpentyl) pphenylenediamine and other phenylenediamines, ketone, ether and hydroxy antidegradants and mixtures thereof, are substantially improved using the process of our invention. Mixtures of antidegradants, for example, a mixture of N 1,3 dimethylbutyl N phenyl p phenylenediamine and N,N bis(1,4 dimethylpentyl) pphenylenediamine, may be used with the activators of this invention.

For the purposes of this invention, sulfur-vulcanizing agent means elemental sulfur or sulfur-containing vulcanizing agent, for example, an amine disulfide or a polymeric polysulfide. The various types of sulfur-containing vulcanizing agents are known to those skilled in the art of rubber 'vulcanization.

The amount of activator required in the practice of this invention depends upon other components in the vulcanizable composition. Generally, after an amount effective to enhance the vulcanization rate is added, additional amounts do not materially affect the vulcanization panameters. The amount of delayed-action activator added is usually between 0.1 to 2.0 parts by weight, the preferred amount being between 0.2 to 0.5 part by weight.

DESCRIPTION OF PREFERRED EMBODIMENTS The intermediates of this invention are prepared from Z-aminobenzenethiols as described in Example 1.

EXAMPLE 1 To a stirred slurry of 43.9 g. (0.3 mole) of S,S'-dimethyl cyanoimidodithiocarbonate [Hantzsch and Wolvenkamp, Ann. Chem. 321, 265 (1904)] in 600 ml. of ethyl alcohol, 75.2 g. (0.6 mole) of o-aminobenzenethiol is added in one portion at room temperature. After a few minutes a clear solution is obtained. The mixture is refluxed for five hours during which time a precipitate forms and methyl mercaptan and ammonia are liberated. After cooling to room temperature, the precipitate is recovered by filtration, washed with 100 ml. of heptane and air-dried at 25-30 C. 74 g. (87% yield) of 2,2- iminobis(benzothiazole) is obtained which melts at 262-263 C. After recrystallization from dimethylformamide, the melting point remains unchanged. Analysis gives 14.70% N and 22.28% S compared to 14.83% N and 22.63% S calculated for C H N S The product is insoluble in water, ether, acetone, chloroform, benzene, heptane, hexane and ethyl acetate and is soluble in dimethylformamide and dimethylsulfoxide. The pKa value of the product determined in a mixture of water and dimethylsulfoxide is 2.5 10- which indicates that the substance is a weak acid.

Substituting 2-amino-5-chloro benzenethiol, Z-amino- 4-chloro benzenethiol, 2-amino-4-nitro benzenethiol, 2- amino-5-hydroxy benzenethiol (4-amino-3-mercapto phenol), 2-amino-4-methyl benzenethiol (Z-amino-p-toluenethiol), 2-amino-4-bromo benzenethiol (2-mercapto-5- bromo aniline) or 2-amino-5-ethoxy benzenethiol in the above procedure gives the corresponding 2,2'-irninobis substituted-benzothiazole) EXAMPLE 2 N,N di(2 benzothiazolyl)cyclohexyl, phenyl or cyclooctylsulfenamides.-To a stirred solution containing 28.3 g. (0.1 mole) of 2,2'-iminobis(benzothiazole) and 15 g. of triethylamine in 200 ml. of dimethylformamide, 0.1 mole of cyclohexyl, phenyl or cyclooctylsulfenyl chloride is added dropwise at 25-30 C. over a 30 minute period. The reaction mixture is stirred at 25-30 C. for 24 hours. After adding 1 kg. of ice water, the solid is collected by filtration and air-dried at 25-30 C. The data are summarized in Table I.

EXAMPLE 3 N,N di(2 benzothiazolyl)isopropylsulfenamide. To a stirred solution containing 0.1 mole of isopropylsulfenyl chloride in ml. of benzene, 0.1 mole of 2,2- iminobis(benzothiazole) and 100 ml. of benzene is added in one portion. After stirring at 2530 C. for 30 minutes, 10.3 g. (0.1 mole) of triethylamine in 50 ml. of benzene is added. The reaction mixture is stirred at 2530 C. for 16 hours, heated at 56 C. for one hour and filtered hot. The benzene is removed in vacuo. The crude product, M.P. l42-146 C., is obtained in 67% yield. After recrystallization from isopropyl alcohol, it melts at l48-150 C. Analysis gives 57.36% C, 4.27% H, 11.51% N and 26.66% S compared to 57.10% C, 4.20% H, 11.82% N and 26.90% S calculated for C H N S The following tables illustrate the improved processing properties obtained by incorporating the new compounds into rubber. For all the rubber stocks tested, as illustrative of the invention, Mooney scorch times at 121 C. and C. are determined by means of a Mooney plastomer. The time (t in minutes required for the Mooney reading to rise five points above the minimum viscosity is recorded. Longer times on the Mooney Scorch test are indicative of greater processing safety. The cure characteristics of the stocks are determined by a Monsanto Oscillating Disk Rheometer at the indicated temperature. The time (t in minutes required for a rise of two Rheometer units above the minimum reading and the time (1 required to obtain 90% of the Rheometer maximum torque are recorded. The difference (t9g'-'t2) is indicative of the cure rate of the stock. Small values of t -t indicate faster cure times. The vulcanization rate K is measured in reciprocal minutes. See Coran, 37 Rubber Chemistry and Technology 689 (1964). Higher values of K indicate higher rates of cross link formation. Vulcanizates are prepared by press curing the stocks at the indicated temperature for the time required to achieve optimum cure as determined from Rheometer data and the physical properties of the Vulcanizates are measured and recorded.

The following natural rubber and styrene-butadiene 6 SBR MASTERBATCH rubber masterbatches are'prepared to illustrate the prop- Oihextended styrene butadiene rubber 1375 erties of the compounds of this invention. All parts are 3 o b h Zinc oxide y Welg Steario acid 1.0 R 5 Furnace carbon black 65.0 NATU RUBBER MASTERBATCH Hydrocarbon softener 1.5

Smoked sheets 100.0 Zinc oxide 3.0 Total 2080 Stearic acid 2.0 10 Vulcanizable compositions are prepared by mixing Furnace carbon black 45.0 sulfur and accelerator with the masterbatches. To some Hydrocarbon softener 5.0 stocks, an antidegradant is also added. The properties of the stocks are determined as previously described and are Total 155.0 shown in Tables II, III and IV.

TABLE I C- N SR Percent Percent H Percent N Percent 8 Empirical Calcu- Calcu- Calcu- Calcu- R M.P. formula lated Found lated Found lated Found lated Found Cyclohexyl-.- 137-139 CgoHnNsS; 4.82 4.75 10.57 10.34 Phenyl 181-183 CauHisNaS: 01.19 01.04 3.59 3.29 10.70 10.92 24.50 24. 79 Cyclooctyl...- 139-140 CzzHzsNsSs .44 5.42 9.87 9.88 22.59 22.00

Recrystallization from heptane-benzene. LReerystallization from ethyl acetate.

TABLE II Stock Number Naturalrubber masterbatch- 155.0 155.0 155.0 155.0 155.0 155.0 155.0 155.0 155.0 155.0 Sulfur- .2 .2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 N- (1 ,3'dimethylbutyDN '-phenyl- 0 0 N-cyclohexyl-2-b enzothiazolesulfenamide 5 5 N-tert-butyi-2benzothiazolesulienamide N-diisopropyl-2-benzothiazolesulienamide 2-(2,6-dimethyl-4-morpholinothio)benzothiazole Benzothiazyl disulfide N,N-di(2-benz0thiazolybbenzenesulfenamide 0. 5 Mooney scorch at 121 0.: t5, min. 18. 0 21. 2 .4 39.4 .0 .0 20.7 Rheometer at 144 0.:

t2 5.1 5.5 7.4 9.6 7.8 .1 7.6 10. 5.4 6.5 t -t 11.9 9.5 14.0 11.9 0.1 .4 16.0 12. 20.1 18. 5 K ,mi11. 0.21 0.24 0.10 0.24 0.145 0.19 0.17 0.22 0.11 0.13 Stress-strain data cured at 144 Cure time, minutes 30 30 40 35 3O 40 300% modulus, p.s.i 1, 520 1,080 1,500 l, 550 1,400 1,300 1, 380 1, 500 960 1,300 Ultimate tensile strength, p.s.1- 3, 500 3,650 3, 700 3,800 3, 280 3, 500 3, 600 3,700 2, 350 3, 300 Ultimate elongation, percent 500 550 550 520 550 570 550 570 550 Shore ".4 hardness 59 60 53 58 55 60 54 57 TABLE III Stock Number Natural rubber masterbatch 155. 0 155. 0 155. 0 155. 0 155. 0 155. 0 155. 0 Sulfur 2. 2 2. 2 2. 2 2. 2 2. 2 2. 2 2. 2 N-(1,3-dimethylbutyl) N-phenyl-p-pheny1enediarnine 2. 0 2. 0 2.0 2.0 2. 0 2. 0 2. 0 2-(2,6-dimethyl-4-morpholinothio) benzothiazoie 0. 5 0. 5 0. 5 0. 5 0. 5

N -diisopropy i2-benzothiazolesulienarnide N,N-di(2-benzothiazoiyl) cyclohexylsulfenamide. N,N-di(Z benzothiazolyl)cyeiooctylsulfenamide N,N-di (Z-benzothiazolyl)isopropylsulienamide Mooney scorch at 121 (3.: t5, Rheometer at 144 0.:

TAB LE IV Stock Number N-(l,3-dimethy1butyl)N-phcnyl-p-phenylenediarnine 2-(2,6-dirnethyl-4-morpho1inothio)benzothiazole 2- (morpholinothio)benzothiazole 2- (morpholinodithio) benzothiazole. N,N-di (2-benzothiazolyl) cycloocytlsulfonarnide N,N-di(Z-benzothiazolyl)isopropylsulfenamide N,N-di (2-benzothiazolyDbenzenesulfenamide Mooney scorch at 135 0.: t min Rheometer at 153 0.:

K 2, m1 Stress-strain data cured at 153 C Cure time, minutes 45 50 45 45 50 30% modulus, p.s.i 8 94 940 960 S1i50 1 010 1 100 1 300 Ultimate tensile strength, p.s.i-

Ultimate elongation, percent"--. 600 590 610 600 620 550 620 590 Shore A hardness 6 66 57 56 57 58 62 60 The data of Table H demonstrate the activity of an ac- 2. A process of claim 1 wherein X is hydrogen. tivator of this invention with different vulcanization ac- 3. A process of claim 2 wherein R is phenyl. celerators. The odd number stocks are controls having 4. A process of claim 2 wherein R is cyclohexyl. accelerator alone whereas the even number stocks con- 5. A process of claim 2 wherein R is isopropyl. tain the delayed action activator. Note that the stocks 6. Avulcanizable composition comprising diene rubber containing the compound of this invention have improved sulfur-vulcanizing agent, an accelerating agent selected processing safety as indicated by the improved Mooney from the group consisting of thiazole accelerators, dithioscorch time and faster curing rates as indicated by the carbamate accelerators, thiuram sulfide accelerators, al- Rheometer data; and that these improvements are dehyde-amine accelerators, diaryl guanidine accelerators achieved without substantially changing the properties of and mixtures thereof and an amount effective to enhance the vulcanizates. the vulcanization rate of the composition of a compound Table III demonstrates the activity of other compounds of the formula of the invention and Table IV demonstrates the appli- S cability of the invention in synthetic rubber compositions.

Although the invention has been illustrated by typical X 0- N-S R examples, it is not limited thereto. Changes and modifications of the examples of the invention herein chosen for 2 purposes of disclosure can be made which do not constiwherein X is hydrogen, lower alkyl, lower y, nitro, tute departure from the spirit and scope of the invention. chloro, bromo, o or y y and n is one or when The embodiments of the invention in which an exclusive is One R is alkyl 0f carbon atoms, Cycloalkyl of property or privilege is claimed are defined as follows: 40 Carbon a afalkyl Of carbon atoms y 1. A process for vulcanizing diene rubber compositions of Carbon atoms; When n is two R is alkylene 0f containing sulfur-vulcanizing agent and an accelerating carbon atoms.

agent selected from the group consisting of thiazole accel- 7- A composition of Claim 6 wherein X is hydrogen. erators, dithio carbamate accelerators, thiuram sulfide 3- A C mposition of claim 7 wherein R is phenyl. accelerators, aldehyde-amine accelerators, diaryl guanidine 9. A composition of claim 7 wherein R is cyclohexyl. accelerators and mixtures thereof which comprises adding 5 1 A C mP ifi II Of claim 7 wherein R is isopropyl. an amount etfective to enhance the vulcanization rate of A mp sition of Claim 7 wherein R is cyclooctyl.

the composition of the compound of the formula References Cited S UNITED STATES PATENTS x /c- N-S R 3,513,139 5/1970 Coran 260-795 B N 2 n JOSEPH L. SCHOFER, Primary Examiner wherein X is hydrogen, lower alkyl, lower alkoxy, nitro, C. HENDERSON In Assistant Examiner chloro, bromo, iodo or hydroxy and n is one or two; when n is one R is alkyl of 1-20 carbon atoms, cycloalkyl of s. CL

5-12 carbon atoms, aralkyl of 7-10 carbon atoms or aryl of 6-12 carbon atoms; when n is two R is alkylene of 1-8 788, 793, 796, 797 carbon atoms and heating at vulcanizing temperature. 

